The paper aims to: 1) CB-839 describe home-made software, based on the IsoBED formula, able to calculate the total dose and the dose per fraction with the same TCP as the conventional fractionation, that will be used with the SIB technique, 2) import the DVHs from different TPSs or different plans, convert them into a normalized 2 Gy-fraction-Volume Histogram (NTD2-VH) and compare these amongst themselves and with the Dose-Volume constraints (DV- constraints), 3) calculate and compare the TCPs

and the Normal Tissue Complication Probabilities (NTCPs) obtained from different DVHs. Methods Radiobiological formulation This approach was based on the LQM, widely used for fractionated external beam-RT, to describe the surviving fraction (sf) of cells in the tissues exposed to a total radiation dose D (expressed in Gy) and to a dose per fraction d(expressed in Gy). The logarithm of the surviving fraction, in the absence of any concurrent re-population, can be expressed as: (1) Where α is a radiobiological parameter, the BED was defined as: (2) and the (α/β) ratio PF-562271 ic50 is a parameter which takes into account the radiobiological effect of fractionation in tumor or OARs. Equation (2) is the basis on which a comparison of different treatment strategies is performed. In order to obtain the same cell survival with two fractionations having a total

dose (D1 and D2) and dose per fraction (d1 and d2), the following equation can be invoked: (3) i.e. (4) and expressed in terms of number of fractions n 1 and n 2 respectively (5) If we have a fractionation schedule with BED 1 characterized by D1, d1 and n1 and a new schedule is required, in terms of n2 and d2, with the same BED

1, then, substituting n2 by n in equation (5) we obtain: i.e. and then (6) The solution of which is: (7) Where d2 is the new dose per fraction delivered in n fractions, resulting in a new total dose D2 = d2 n, Equation (7) is valid for both PTVs and OARs (following the LQM). The IsoBED Selleck LB-100 software The software has been developed using the Microsoft Visual Basic 6.0. The main form – the IsoBED Calculator- gives a choice between IsoBED calculation and DVHs analysis modules. IsoBED Calculation The software allows the anatomical district to be selected. The user has to introduce the total dose, Galeterone dose per fraction (generally 2 Gy per fraction) for each target (up to 3) and, the (α/β) ratio of investigated tumor must be inserted to calculate the corresponding BED. Then the software requires the selection of the reference target (which determines the fractions number in the SIB treatment), in order to calculate the new fractionation for the remaining targets, based on equation (7). Furthermore, the software permits a comparison of the biologically equivalent schedules using hyper/hypo-fractionated as well as conventional regimes.